Genetic defects underlying several degenerative muscle diseases such as Duchenne muscular dystrophy (DMD) are known, yet effective therapies for these disorders have not been found. One approach has been cell-based therapy in which normal myoblasts or genetically modified patient myoblasts are injected into diseased muscle with the intent that engraftment would be sufficient to compensate for protein deficiencies. Little success has been achieved with this approach however due to problems such as poor graft survival and impractical requirements for numerous muscle injections. Recently, systemic delivery of muscle precursor cells via tail vein or arterial injection in mice has been demonstrated resulting in low-level donor cell engraftment of regenerating muscle tissue. Vascular migration and extravasation of precursor cells thus occurs and could provide a useful route for improved cell-based therapy for these devastating diseases. The specific aims of the proposed work are to 1) Identify molecules expressed in myoblasts that are involved in the attachment to activated endothelial cells and promote trans-endothelial cell migration, 2) Improve the efficiency of myoblast trans-endothelial migration, if possible, by cytokine-induced expression of molecules known to regulate attachment and extravasation of immune system cells. Methods: Murine skeletal muscle myoblasts will be studied to determine expression levels of proteins known to function in leukocyte extravasation. Inflammatory cytokines will be used to induce myoblast expression of proteins relevant to chemotactic movement. In vitro trans-endothelial cell migration assays will be used to assess the role of specific chemokines, receptors and cell adhesion molecules in this process and the influence of inflammatory cytokine stimulation on myoblast migration. Normal myoblasts and those induced by cytokines will be injected into tail veins of mdx mice (model for DMD) undergoing muscle regeneration and extravasation into tissues assessed. Results will further our understanding of the mechanisms that promote systemic engraftment of donor myoblasts into diseased muscle could significantly advance the therapeutic use of myogenic precursor cells for the treatment of muscular dystrophy.